Rigid and inflexible and strongly enforced government standards exist in the control of the pharmaceutical and/or health industry in the testing equipment and accuracy and consistency thereof and reliability thereof, (1) for permeability of transdermal membrane(s) of unknown permeability to one or more liquid(s) of known permeability capability(ies) and/or (2) for the permeability of one or more liquid(s) of unknown permeability capability(ies), to a transdermal membrane of known permeability capability(ies), and/or (3) for the testing of a non-liquid matter of known absorption rate to either a transdermal membrane of unknown permeability with a liquid of known permeability, or for the testing of a non-liquid matter of unknown absorption rate to a transdermal membrane of known permeability using a liquid of known permeability. Factors that are critical to the obtaining of consistent test results typically include the exact volume of liquid in the testing vessel surrounding the transdermal cell, its volume being always a "constant", i.e. the volume of liquid being the same from one test to the next, as a known unchanging constant. Another such factor that can alter the repeatability of test results, is the presence of different pressure of a solute and/or non-liquid matter within a constant-volume reservoir, from one test to another, arising from use of different quantities of the non-liquid matter in different otherwise repetitive tests; such non-constant condition results and arises from availability of different amounts of the same or different non-liquid matter to be tested in otherwise repetitive tests when consecutive identical tests use the same or identical transdermal membranes. The same problem results if the volume of the reservoir for holding the non-liquid matter, varies from one test to another for otherwise identical quantities (volumes) of the non-liquid matter(s) being tested and/or retested for verification. Accordingly, great care heretofore has been essential to assure consistent and reliable repetitive results in testing the same non-liquid matter, or in tests using different non-liquid matter for comparative purposes. Unfortunately, such government requirements are difficult to meet repeatedly with the required degree of accuracy. As set-forth in the following objects, the present invention is directed principally to overcoming such typical prior difficulties in achieving consistent and repeatable results for liquid(s) and/or transdermal membrane(s) and/or non-liquid matter(s) - as the case may be, being tested.